The title compound, (C(6)H(11)N(2))(4)[Mo(8)O(26)] or (emim)(4)[β-Mo(8)O(26)] (emim is 1-ethyl-3-methyl-imidazolium), was obtained from the ionic liquid [emim]BF(4). The asymmetric unit contains two [emim](+) cations and one-half of the [β-Mo(8)O(26)](4-) tetra-anion, which occupies a special position on an inversion centre. The β-[Mo(8)O(26)](4-) tetra-anion features eight distorted MoO(6) coordination octa-hedra linked together through bridging O atoms.